The invention relates to an optical system for a stereoscopic surgical microscope for interchanging two parallel light rays with simultaneous image reversion for both rays without parallel offset of the emerging pair of rays with respect to the entering pair of rays, comprising elements reflecting on one side and two elements reflecting in parallel on both sides, all arranged in a plane perpendicular to the incident rays, each of the elements reflecting on both sides reflecting with its front side the incident ray via the elements reflecting on one side to the rear side of the respectively other elements reflecting on both sides.
Prism systems for stereoscopic image erection of this type are known (DE-C 38 26 069). From the viewpoint of application technology, it is desirable to accommodate the optical arrangement in the microscope in a way which saves as much space as possible. To avoid undesired light losses, it is endeavoured to obtain shortest possible optical path lengths within the device. Since surgical microscopes are generally mounted movably to allow them to be oriented freely, but nevertheless have to be fastened stably, the weight of the microscope must be kept down as much as possible.